Such inflation devices are used for injecting a fluid into a balloon that has previously been placed, while in the contracted state, inside an artery or a vein of a patient. Such devices are described, for example, in U.S. Pat. No. 5,147,300.
Such devices are used in particular for percutaneous transluminal angioplasty, in particular for the purpose of dilating the artery or the vein in which the balloon is disposed.
Inflation devices must be capable of delivering high pressure, of the order of 30 bars. Under the action of such pressure, the piston is subjected to a large axial force which, in the absence of manual pressure on the free end of the piston, needs to be contained by the half-nut(s) co-operating with the thread.
In addition, particularly when the device has only one half-nut as described in the above-mentioned US patent, the member for controlling said half-nut is formed by a rod whose end is deformed into a crank shape. This end is engaged in a slot of the half-nut so as to cause it to move sideways when the rod is moved axially along the syringe body.
Because of the high pressure that exists inside the syringe, which pressure exerts a high axial thrust force on the piston, releasing the half-nut requires a large amount of force such that the control rod tends to become deformed without performing its function of moving the half-nut in satisfactory manner. It is therefore necessary to make the control member out of a material that is extremely rigid, thereby increasing the cost of manufacturing the device.
In addition, the control rod of that device is moved by drive from one of the practitioner's thumbs on a mechanism for driving the rod in translation. However, it is often difficult to release the half-nut while pressing with one thumb only. In other words, the device is not very ergonomic.